By way of background, a battery operated digitizer tablet was designed as a data processing device for entering digitized data into a data processing system. The data is created by manually moving a stylus over a tablet similar to handwriting on a pad. The tablet includes a power management system to increase battery life between charges. The tablet also included a light emitting diode (LED) that is turned on when a part of the circuitry is powered on. The LED is turned off when such circuitry is powered off. The tablet also includes a volatile memory that contents of which is stored before turning off the power to such circuitry. Quite obviously, the battery should not be removed before saving the volatile memory contents, and the LED thus provides a signal warning the user not to remove the battery until the light is turned off.
Data processing devices commonly use lights to inform the user. The lights are typically placed on the front or top of a housing in full view of the user. Unfortunately, the lights may be ignored, not seen, misinterpreted, etc. allowing mistakes to occur. When a light is used as a warning to not do something or else adverse results will occur (e.g., don't remove the battery or else you might lose data), it was felt that a more positive approach had to be taken other than by simply placing the light on the front of a housing.